Rational Design of a Chemical Bath Deposition Based Tin Oxide Electron-Transport Layer for Perovskite Photovoltaics.

Chemical bath deposition (CBD) is widely used to deposit tin oxide (SnO ) as an electron-transport layer in perovskite solar cells (PSCs). The conventional recipe uses thioglycolic acid (TGA) to facilitate attachments of SnO particles onto the substrate. However, nonvolatile TGA is reported to harm the operational stability of PSCs. In this work, a volatile oxalic acid (OA) is introduced as an alternative to TGA. OA, a dicarboxylic acid, functions as a chemical linker for the nucleation and attachment of particles to the substrate in the chemical bath. Moreover, OA can be readily removed through thermal annealing followed by a mild H O treatment, as shown by FTIR measurements. Synergistically, the mild H O treatment selectively oxidizes the surface of the SnO layer, minimizing nonradiative interface carrier recombination. EELS (electron-energy-loss spectroscopy) confirms that the SnO surface is dominated by Sn , while the bulk is a mixture of Sn and Sn . This rational design of a CBD SnO layer leads to devices with T ≈1500 h, a significant improvement over the TGA-based device with T ≈250 h. The champion device reached a power conversion efficiency of 24.6%. This work offers a rationale for optimizing the complex parameter space of CBD SnO to achieve efficient and stable PSCs.